1. Field of the Invention
The present invention relates generally to an automatic power transmission for an automotive vehicle. More specifically, the invention relates to a system for detecting failure in the automatic power transmission.
2. Description of the Background Art
Self-diagonosable automatic power transmissions which are provided with self-checking functions for detecting failure in shifting or so forth, have been developed in various fashions. For example, "Nissan Full-Range Electronically Controlled Automatic Transmission RE4R01A Service Manual", published by Nissan Motor Co., Ltd., in Mar. 1987, shows one example of a self-diagonosable automatic power transmission, which performs self-checking for identifying sensor, actuator, control unit or so forth, causing failure when failure of the transmission occurs. However, the self-checking function provided for this type of transmission is intended to be used for trouble shooting in the service station or factory. Therefore, the self-checking function is not effective for a driver to detect occurrence of failure. Therefore, when one component in the transmission or a transmission control system fails, such failure is difficult to detect. Therefore, it is possible that the failure of one components leads to severe failure in other components.
For example, when the fluid pressure in the forward clutch abnormally drops for causing slip in the forward clutch, the driver may not realize the failure in the pressure supply for the forward clutch and thus continue driving. In this circumstance, the driver may continue stepping on an accelerator pedal firmly to compensate for a drop in vehicle speed, so that clutch plates are maintained in a slipping state for causing substantial heat which results in seizure. Once the clutch plate causes seizure disconnection of the torque converter from the transmission gear via the clutch becomes impossible so that the driving power is still transmitted to the power train at the selector position commanding N range.